Re: ? Overloaded Auto Chromatic Tuner

Alec S. <google.forums@xxxxxxxxxxxxxxxx> wrote in message
news:1158000903.061342.125860@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Hi,

I have a Matrix auto chromatic tuner-to tune instruments-model
SR-4000.

A while back I killed it by-accidentally, I swear!-plugging in a
power cord which was set to a few volts too high (12v instead of 9v)
backwards (reversed polarity).

I would like to fix it. I would like to diagnose the problem and if
I'm lucky repair it (I assume it's a dead component that needs to be
replaced.)

While I am no electronics expert, I am also not a novice. I have
repaired computer hardware (and built a few parts of my own), and even
our home's wiring (although that's really just dangerous, not complex.)

I've got a digital multimeter, variable power supply, all kinds of
wires, alligator clips, etc, hopefully pretty much any tools I might
need. I've also got a large box full of electronic part potpourri that
I got from various places including a supplier a long time ago and from
various electronic devices I've cannibalized.

I have scanned the circuit board and they can be found here:
http://img378.imageshack.us/img378/4002/chromatictunerfrontbo8.png
http://img230.imageshack.us/img230/8016/chromatictunerbackag3.png

I've tried running a couple of small tests, but I don't really know how
to test something like this. For example, I'm not certain how to test
if a transistor is good (I've got an idea but I'd rather hear from
experienced people), or a quick connectivity test reveals nothing
useful since pretty much everything seems to be connected to everything
else, and testing for power returns all kinds of variable voltages that
tell me nothing.

Does anyone have any tips or advice (or maybe a complete walkthrough?)
on how to test and repair this?


Thanks a lot!

--
Alec S.


from my file
http://www.divdev.fsnet.co.uk/repair2.htm

Matrix SR 4000 auto chromatic guitar tuner, 1993?
Owner had connected an external 9V ps reversed
and knocked out the 78L05 as no reverse protection.
Replaced V Reg and cut trace to switch to put
a small 150mA diode in line
I was intrigued by another 3 pin TO92 device marked
8054
HN
3C31
Presumably working order - just wondered what it did.
Probably 8054HN not 8054 datecode , by Seiko,
activation voltage 3.8V to 4.2V, battery monitor.
One line is connected to INVERSE READ of the 80C51 micro
, I didn't trace any other lines.
Seems odd having this sophistication to hold
the micro from erroneous but not fatal operation
but no diode protection against battery or ext ps reversal,
especially in a product destined for musos.

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/



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